The present invention relates to systems for containing animals within a specified boundary. Specifically, the invention increases the security of a boundary defined by a buried cable carrying an alternating current, which is used to discourage the animal from crossing the boundary.
Electronic animal control systems to confine an animal within a predefined perimeter or boundary are in current use. The area of confinement is defined by a buried conductor which carries an alternating signal current. The animal, such as a household pet, carries a small receiving device connected to a collar which detects a magnetic flux emanating from the buried conductor. As the animal approaches the conductor, the magnetic field associated with the buried conductor induces a corresponding alternating current in a induction coil or antenna worn by the animal. As the animal approaches the buried conductor, the magnitude of the induced current increases, and when the voltage across the induction coil reaches a threshold voltage, the receiver will trigger an alarm, or electric shock to the animal to warn the animal that it is approaching the boundary.
These systems are widely popular, and are effective in most situations. However, in times of excitement, such as a dog chasing another animal, the dog may lunge across the boundary, as the corrective action is applied too late, or with a duration which is too short.
As an additional problem, the antenna or induction coil used to detect the presence of a magnetic field produced by the current in the buried conductor tends to be directional. Thus, if the animal approaches the conductor at the proper angle, it is possible that only a minimum amount of flux is coupled to the induction coil, and the receiver will fail to detect the resulting insignificant voltage. Thus, depending on how the animal approaches the boundary defined by the buried conductor, it may be possible to escape from the perimeter without receiving any warning stimulus.
As a solution for avoiding any null or insufficient signal as a result of the orientation of the induction coil antenna with respect to the buried cable, three orthogonal antennas may be used together, as shown in U.S. Pat. No. 5,425,330. The three antennas having the orthogonal orientation are sampled constantly, and the larger of the three signals produced from the antennas is utilized to detect the presence of the animal near the buried conductor. Even in the multiple antenna coil system, however, there still remains a significant difference in the detected signal strength for the range of orientations which the animal may have with respect to the buried conductor. While the problem may be reduced by including even more antenna coils, the increased number of antenna coils increases the cost, circuit complexity and bulk associated with the device.